1. Contribution from the Department of Chemistry, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan, Chemistry Division and Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois 60439, and CREST, Japan Science and Technology Agency (JST), c/o Department of Chemistry, Keio University, Yokohama 223-8522, Japan